Ocean Biodiversity Barely Changed for Hundreds of Millions of Years: Study
Fri, December 9, 2022

Ocean Biodiversity Barely Changed for Hundreds of Millions of Years: Study


The world’s oceans are home to millions of species. Taking care of them to maintain a healthy ecosystem plays a huge role in climate regulation. The health of the oceans is strongly dependent upon marine biodiversity. However, just like other ecosystems, oceans are heavily affected by climate change. Human-induced warming has altered marine species’ abundance, diversity, and distribution, thus, affecting ocean biodiversity. 

A 2019 study presented the first comprehensive map of risks to biodiversity in the ocean. To map the average conservation status of marine biodiversity, the researchers used the range and extinction risk data of 5,291 marine species on the Red List of Threatened Species by the International Union for Conservation of Nature (IUCN). The IUCN systematically assesses species and classifies their risk of extinction as “least concern,” “near threatened,” or “threatened.” The last category includes “vulnerable,” “endangered,” and “critically endangered.”

According to the World Economic Forum, an independent international organization committed to improving the state of the world by engaging business, political, academic, and other leaders of society to shape global, regional, and industry agendas, the findings of the study revealed that barely 0.1% of the ocean was truly at least concern for extinction. At least a quarter of the 83% species of the ocean are threatened. The researchers found the highest risks to biodiversity in regions like the Mediterranean and Black seas.

“Biodiversity is actually a complicated collection of ideas. The metrics we usually use don’t take into account conservation status. So what we’re doing is adding the IUCN conservation status into the mix, which provides an additional filter for looking at biodiversity,” Casey O’Hara, a doctoral student at the Bren School of Environmental Science & Management at the University of California, Santa Barbara, said. 



Levels of Ocean Biodiversity Hasn’t Substantially Increased

Previous studies showed that due to sustained increases over the last 200 million years in oceans, marine diversity today is higher than ever. Most of them have historically focused on estimating how “global” diversity changed through time. However, a team led by researchers from the School of Geography, Earth and Environmental Sciences at the University of Birmingham rejects this and calls so-called "global" diversity curves misleading. 

Lead author Dr. Roger Close, a paleobiologist at the University of Birmingham in the UK, said that the problem with these studies was that the fossil record they used wasn’t global because both the amount and the parts of the world that are actually preserved in the fossil record changes so much through geological time. Thus, they conducted a study to correct this. 

According to Phys.org, an internet news portal that provides the latest news on science, the researchers studied diversity at regional spatial scales using fossil data collected over the past 200 years. They compiled these data in the Paleobiology Database over the last 20 years and focused on places and times that are well-known in the fossil record. The team was able to show regional-scale patterns of diversity across geological time from the so-called Cambrian Explosion to the present day. They also showed how marine animal diversity varied across both time and space by comparing geographic regions that were similar in size.

The findings revealed that instead of increasing continuously over the last 200 million years, levels of biodiversity in our oceans have remained fairly constant. This is a major departure from previous studies of "global" diversity. These studies concluded that marine animal biodiversity had increased steadily over the last 200 million years, culminating in modern levels that were greater than any point in Earth's history. In contrast, our work suggests that modern levels of biodiversity—at least at the regional scales we studied—are not exceptional,” the researchers said. 

The study, however, observed one point in the fossil record where there was a step change in diversity. This happened at the end of the Cretaceous period, when the dinosaurs became extinct, 66 million years ago. According to Newsweek, an online site that provides in-depth analysis, news, and opinion about international issues, technology, business, culture, and politics, the mass extinction was followed a dramatic shift in biodiversity levels with an expanding roster of new species that took advantage of the space left behind.

"We find a rapid recovery of diversity levels after the last mass extinction 66 million years ago—in fact, to levels even higher than before (although the time resolution of our study is fairly low). Past work has suggested that biodiversity would recover from anthropogenic extinction within a few million years,” Close said. 

Additionally, the researchers noticed coral reefs historically displaying some of the greatest variety of species. In a statement, Close said that we could see fluctuations in diversity that are often substantial to them. "Some groups might benefit from the misfortune of others, but the overall levels of diversity that we see have remained fairly stable for hundreds of millions of years,” he said. 



The Decline in Ocean Biodiversity

The 2019 Global Assessment Report on Biodiversity and Ecosystem Services revealed that extinction rates of marine species have accelerated sharply in the past century. More than half of the world’s marine species could be on the brink of extinction by 2100 without substantial actions to combat climate change. This could mean a much worse decline in ocean biodiversity, hindering the ocean's ability to provide food for our growing population. 

According to NRDC.org, a non-profit international environmental advocacy group, the findings revealed that over one-third of marine mammals and nearly one-third of sharks, shark relatives, and reef-forming corals are threatened with extinction. Climate change is expected to decrease ocean net primary production between 3% and 10% and fish biomass by 3% to 25% by the end of the century. Prof. Roberto Danovaro, president of the Stazione Zoologica Anton Dohrn in Naples, Italy, said that the good news is that ecosystem restoration in oceans can cause species that disappeared from a particular region to return. This means that there’s a possibility that ecosystems could recover from the damage caused by industrial development.

"This is an opportunity not to stop (building) infrastructure but to find a solution to encourage blue growth (economic growth in the marine sector) development along with biodiversity conservation and habitat conservation," Prof. Danovaro said.